Oil-based muds form a general class of materials that minimally comprise a mixture of particulate solids in an oil-continuous phase. A subset of oil-based muds is oil-based drilling muds, which contain functional fluids used to improve drilling operations in several ways. These fluids are circulated through and around the drill bit to lubricate and cool the bit, provide flotation to help support the weight of the drill pipe and casing, coat the wellbore surface to prevent caving in and undesirable fluid flow, and to carry drill cuttings away from the bit to the surface. Such oil-based drilling fluids are oil-continuous compositions that may also contain an aqueous solution (e.g. calcium chloride brine) as a discontinuous phase (making the fluids water-in-oil inverse emulsions), emulsifiers to stabilize the inverse emulsion, rheology modifying agents (e.g. oleophilic clays), weighting agents (e.g. barium sulfate), fluid loss control agents (e.g. lignins), and other additives (e.g. lime). Used oil-based drilling muds will contain, in addition to the above components, drill cuttings and other dissolved or dispersed materials derived from the drilled medium or from other sources of contamination such as process and environmental waters. Waste oil-based muds are simply used or contaminated oil-based drilling muds containing a sufficient concentration of drill cuttings or other components to warrant either a disposal or a recycling of the mud.
Waste management of oil-based drilling muds, made with either diesel or synthetic oil, is a high priority for companies drilling both onshore and offshore wells. The current trend in managing these waste oil-based drilling muds (i.e. drilling fluids laden with cuttings) is moving towards reclamation and recycling of the muds. Much of this trend is a response to regulation. Reclamation and recycle of these fluids almost always requires a good separation of the oil phase and possibly the aqueous phase from the oil-based drilling muds.
The methods used for solid-liquid separation of oil-based drilling muds (OBDMs), have included mechanical, thermal and some chemical treatments. The chemical treatments include the use of: sodium silicates in U.S. Pat. No. 2,476,846; organic solvents in U.S. patent application Ser. No. 4,040,866; a neutralization-flocculation scheme in which a dissolved polymeric flocculant was employed in U.S. Pat. No. 4,482,459; polyethylene oxides to dewater OBDMs (Sharma, S. K. and A. G. Smelley (1991) “Use of flocculants in dewatering of drilling muds.” Advances in Filtration and Separation Technology 3 (Pollution Control Technol. Oil Gas Drill. Prod. Oper.) pp 43-51); water and surfactants or oil washes in U.S. Pat. No.5,090,498; carboxylic acids in combination with pH cycling in U.S. Pat. No. 5,156,686; supercritical fluid extraction (Eldridge, R. B. (1996) “Oil Contaminant Removal from Drill Cuttings by Supercritical Extraction.” Industrial & Engineering Chemistry Research 35(6): 1901-1905); surfactants with pH adjusters in U.S. Patent Application Publication No. 2003056987 A1, and acid treatment followed by a dissolved water-soluble polymer in U.S. Patent Application Publication No. 2003083532 A1.
In a thesis by Julio Oswaldo Bello Torres and Luis Hernando Pérez Cárdenas entitled “Analisis TecnicoEconomico de un Metodo FisicoQuimico Alternativo Para la Separacion de Agua y Solidos en Lodos Base Aceite”, Fundacion Universidad de America, Santafé De Bogotá, D. C. (1999), both solid and water-in-oil emulsion polymer flocculants were diluted in water at about 3% by weight concentration and then mixed with OBDMs. None of the polymer flocculants were directly or neatly mixed with OBDMs prior to dilution with water.
While the above treatments may be used to some extent in the separation of particulate solids from OBDMs, they each have their own drawbacks, whether it be in terms of process inefficiency, the generation of additional volumes of waste to be treated, or lack of economic viability.
The inventors of the present invention have discovered that the direct use of neat or oil-diluted water-in-oil emulsions in which the discrete phase contains a polymer comprising at least one water-soluble monomer provides excellent separation of oil from oil-based drilling muds. This is rather surprising since there are some documents that have statements that indicate a lack of utility of water-soluble polymers in treating OBDMs (e.g., Field, S. D., A. Wojtanowicz, et al. (1987) “Deliquification of oilfield drilling slurries and production sludges.” Proceedings of the Industrial Waste Conference, 41st: pp 481-7).